Thoroughly Disturbing
I think that the entire mood started off perfectly. The lack of music made the ehthereal, airy sounds much more prevelant and keep the viewer focused on the action.
When I saw the clown I found the fact that his eyes were always in motion made them stand out, attracting attention to them made it creepier. Not to mention the brilliant art of the enitre animation throughout.
When the bug crawls through the clown you can almost feel it, it's uncomfortable and that's just what it should be.
The stomach spitting the bug out was a nice, gross touch.